It is widely recognized that the manually-operated seat belt systems with which most vehicles presently in use are equipped are often not used. Many people tend not to use manually-operated safetly belts because they either find it inconvenient or troublesome to fasten them when they get into the vehicle and unfasten them when they get out or they find them uncomfortable or somewhat restrictive of movement. Because of the reluctance of people to use manually fastened seat belt systems, government and industry are moving in the direction of requiring and furnishing, respectively, passive safety belt systems, i.e., belt systems which automatically move to an occupant-restraining position when the occupant enters the vehicle and automatically move to an occupant-releasing position when the occupant leaves the vehicle. Advantageously, such passive safety belt systems should require a minimum amount of space, contribute a minimum amount of weight, complexity and cost to the vehicle, should operate reliably with absolutely no margin of error and should provide for prompt and simple release in an emergency. Fulfilling all of these requirements is difficult.
The desirability of providing for emergency release of the restraint belt system has, of course, a somewhat deterimental effect; the provision of an emergency release buckle can defeat the basic purpose of a pasive system, namely, the complete assurance that the occupant will use the restraint belt, inasmuch as the occupant can unfasten the belt using the emergency release buckle. An object of the present invention is to counteract the effect of the emergency release buckle as a means by which the occupant can avoid the use of the restraint belt. A further object of the invention is to improve the reliability of the system by warning the occupant of a possible malfunction so that steps can be taken to correct the malfunction rather than to present a risk of the failure of the system to restrain the occupant in the event of a collision in the circumstance of an otherwise unknown malfunction. The invention also provides a system that is particularly suitable for the so-called hard-top type of vehicle, i.e., a vehicle that does not have a center pillar.